This invention relates to a continuous bucket elevator which is used in a method of separating non-coal impurities from raw coal and, more particularly, to structure for linking the buckets together
In the operation of a conventional coal washbox, coal is separated into various sizes and the segregation of refuse material is effected in a liquid medium by a pulsating movement of the liquid to produce back and forth surging motion within each cell of the washbox alternately to distend and then settle the material being treated while being supported on screens or perforated plates. Most non-coal impurities have specific gravities greater than coal. Such differences in specific gravity provide the basis for mechanical separation of coal from the non-coal refuse. As material progresses through the washbox, heavy refuse material and middlings are separated therefrom and delivered to continuous bucket elevators which remove the waste material from the washbox. In addition, the elevators are used in the removal of fine silica particles in the hutch material. Buckets currently used in such elevators have parallel vertically disposed side steel plates which are connected by U-shaped screening plates having a plurality of openings through which hutch water including the silica material tends to drain as the elevator removes the refuse material from the washbox. The elevator also includes two elevator chains which have the buckets secured thereto and chain links thereof are received by sprockets provided at the upper and lower ends of the elevator compartment. For securing the buckets to the elevator chains, each bucket is provided with four bushings, two on each side, one at the upper aspect and the other at the lower aspect of each side.
Depending on the extent of its use and the nature of the raw coal being processed, a washbox is expected to perform in cycles of seven to ten months with ordinary maintenance and adjustments being made during each cycle. At the end of each cycle, the washbox is taken out of operation and worn parts are replaced in a major renovation. Because of the abrasive characteristics of the material and, particularly the hutch material, components of the washbox are subjected to excessive wear and many must be replaced at the end of each cycle.
An elevator bucket, as such, should last for two to three cycles. Nevertheless, repairs are required between cycles and the major repairs involve the chain links and bushings. Rather than risk unscheduled repairs during an operation cycle, it is not uncommon to replace the entire chain assembly at the end of each cycle.
As the chain assembly is subjected to ordinary wear during an operating cycle, it is retained in proper tension by adjusting rods at the head of the bucket system. When the adjustment reaches its limits, a bucket may be removed from the system whereupon the adjusting rods are lowered and the chain is again tightened to the proper amount of tension.
Replacement of the chain at the end of each cycle and repair or replacement of the bushings involve a considerable investment in time and expense. Nevertheless, for many years this investment has been part and parcel of washbox repairs and component replacements considered necessary or advisable at the end of each operating cycle.
Two patents which disclose coal washboxes of a type in which the instant invention may be installed, are U.S. Pat. No. 2,609,098 of C. Lotz issued Sept. 2, 1952 and U.S. Pat. No. 2,666,525 of R. Pate which issued Jan. 19, 1954. The latter is assigned to McNally-Pittsburg Manufacturing Corporation of Pittsburg, Kans. McNally has manufactured washboxes for a number of years including the McNally Norton Standard washer, the McNally Giant washer, the McNally Mogul washer and the McNally-Norton Unit Washery, all of which have continuous bucket type elevators. Steel washbox chains are available from the Rexnord Mechanical Power Division, Engineering Chain Operation, of Milwaukee, Wis. and Westran Corporation Manganese Cast Chain Division of Muskegon, Mich. Elevator buckets are available from McNally Pittsburg Mfg. Corp. in various sizes from less than one foot width to widths in excess of four feet. Various types of bucket elevators are well known in the art. They include Caldwell elevators, Gifford-Wood Co. apron conveyors, Jeffrey V bucket conveyors, Peck carriers for coal and the like, Centrifugal discharge-type bucket elevators, Perfect discharge-type bucket elevators, continuous bucket elevators on single-strand chains or belts, super-capacity continuous bucket elevators on double strand chains as well as others. The state of the art is exemplified by the following U.S. Patent Nos. 119,580; 289,466; 645,175; 1,583,221; 1,671,571; 1,725,506; 2,335,166; 2,620,575; 2,631,459; and 4,000,568.